Sealing arrangement

ABSTRACT

A face seal acts across a gap between first and second machine, particularly a gas turbine, components operating at elevated temperatures. One end of a sealing element is housed in a recess in the first component and its other end seals against a plane surface of the second component under the action of a spring. To allow assembly of the components and the seal within, say, a gas turbine engine without damaging the seal or other components, the sealing element is temporarily retained entirely within the recess by a latch, the latch being temperature-sensitive and operative only once to release the sealing element to perform its sealing function at a predetermined elevated temperature. The latch may be a fusible pin.

FIELD OF THE INVENTION

The present invention relates to seals suitable for obturating a gap between machine components, e.g., of a gas turbine. It particularly, but not exclusively, relates to face seals.

BACKGROUND OF THE INVENTION

Various forms of sealing arrangements are required in gas turbines to control unwanted leakage of gas (either compressed air or combustion gases) from one part of the turbine structure to adjacent parts that are at lower pressures. Such sealing arrangements must be operative at the elevated temperatures at which gas turbines typically operate. One example of a part of a gas turbine requiring such a sealing arrangement is shown in FIG. 1 of the accompanying drawings.

The requirement here is for a so-called “face seal” to restrict leakage of gases through the gap G between components 12 and 14. To accomplish this, an elongate sealing element S has one end face A which is sealingly captured and housed within a recess R in component 12 and whose other end face B sealingly engages the planar face 24 of component 14, thereby substantially obturating the gap G between components 12 and 14. To achieve and maintain an effective seal throughout the operating cycle of the gas turbine, sealing element S is spring-urged against face 24 of component 14 by virtue of a spring 26 held within recess R of component 12. To cope with vibration or relative sliding movement between components 12 and 14 and to avoid damaging the face 24 of component 14, the end face B of the sealing element S may be given an abradable or anti-wear coating C that is less hard than the material of which component 14 is made.

Such a spring-urged face seal is effective to reduce and control unwanted gas leakage. However, problems arise in that when the sealing element is inserted into recess R in component 12 before or during assembly of components 12 and 14 into the turbine, the sealing element S must be temporarily retained completely within recess R, not only to protect the sealing element S and its end face B against damage, but also to protect other components. Once the turbine has been assembled, the components 12 and 14 and sealing element S are not accessible, therefore a means must be provided to release the sealing element from capture within recess R, without direct human intervention, so that it can perform its sealing function.

SUMMARY OF THE INVENTION

The invention contributes to solving the above problem by providing a fusible pin or other temperature-sensitive retention means to enable a once-only actuation of a face seal after assembly of the turbine or other machine operating at elevated temperatures.

According to the present invention, a sealing arrangement for acting across a gap between first and second machine components operating at elevated temperatures comprises:

a sealing element having a first end captured within the first component and a second end able to seal against a surface of the second component,

spring means acting between the first component and the sealing element to urge the sealing element towards the second component, and

retention means for temporarily retaining the sealing element within the outer dimensions of the first component, the retention means being temperature-sensitive and operative only once to release the sealing element to perform its sealing function at a predetermined elevated temperature.

In the context of the above-stated prior art problem, it will be seen that the elevated temperatures at which the machine components operate will be the normal operating temperatures of the part of the gas turbine in which the components are located, and the predetermined elevated temperature at which the sealing element is released will be a temperature below the components' normal operating temperature by an amount sufficient to ensure a reliable “once only” release action during first run of the gas turbine.

In the preferred embodiment, the temperature-sensitive retention means is at least one detent that at room temperature restrains the sealing element against the action of the spring means, but which at the predetermined elevated temperature fails by softening, melting or charring of the material of which it is made, thereby releasing the sealing element. The detent conveniently comprises a fusible latch, such as a pin or the like that is held in the first component and that projects into or through the sealing element.

It is particularly envisaged that the invention will be of use in sealing between gas turbine components, such as internal casings, in which the first and second components are annular, the gap between them is defined by respective confronting annular faces of the first and second components, and a plurality of sealing elements are arranged in a circle that extends around the confronting annular faces.

Further aspects of the invention will be apparent from a perusal of the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side elevation of a prior art sealing arrangement to restrict leakage of gases between first and second turbine components;

FIG. 2 is a sectional side elevation of a sealing arrangement in accordance with the present invention, showing a sealing element retained in a non-operative position; and

FIG. 3 is a view like FIG. 2 but showing the sealing element acting as a face seal in an operative position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, a sealing arrangement 10 in the form of a face seal acts across a gap G between first and second machine components 12 and 14, respectively. The components are part of a gas turbine operating at elevated temperatures. For example, components 12 and 14 may be adjacent internal turbine casings within an outer casing of a gas turbine engine, the casings having confronting plane annular or part-annular faces 23 and 24.

Component 12 has a deep recess 16 formed in it, which houses an elongate sealing element 18 having a first end 20 captured within the recess and a second end 22 able to seal against a face 24 of the second component 14. A spring 26 is trapped between the inner end of the recess 16 and the sealing element 18 and acts to urge the sealing element towards component 14.

At normal operational temperatures of the turbine, the wear-coated end 22 of the sealing element 18 is urged into contact with the face 24 of component 14 by the spring 26, but to allow assembly of the components 12 and 14 into the turbine without damaging the seal element or any other parts of the turbine, the sealing element is temporarily retained wholly within the recess 16 until assembly is complete and the turbine is ready for testing. The task of retaining the sealing element 18 within component 12 is accomplished by a temperature-sensitive detent or latch 28, the latch being operative only once, at a predetermined elevated temperature, to release the sealing element to perform its sealing function.

In the present embodiment, the latch 28 comprises a fusible pin made of a low melting point alloy, such as “Cerrobend™”. This has a nominal composition of Bismuth 50%, Tin 13.3%, Lead 26.7%, Cadmium 10.0%, Tin 13.3%, with a melting point of 70 degrees Celsius. Other low melting point compositions would be suitable, provided their melting points are well above room temperature but well below turbine operating temperature. To accommodate the pin 28, a blind hole 30 is drilled in component 12 during manufacture, the pin being a sliding fit in the hole. The hole 30 extends at right angles through the recess 16, so that when the sealing element 18 is inserted with its end 22 flush with the surface of component 12, a suitably positioned slightly larger hole 32, previously drilled in the sealing element, comes into registration with hole 30. Hence, pin 28 can be inserted through the sealing element to hold it temporarily in position. After assembly of the turbine, and when its temperature increases to 70° C., the pin 28 melts and the sealing element is released under the action of the spring 26 to perform its sealing function.

As an alternative to the use of a low-melting point metallic pin 28, a fusible thermoplastic pin could perhaps be used instead. As a further alternative, a pin made of a thermosetting plastic that chars and/or becomes very brittle at elevated temperatures might be used.

To prevent undesirable release of the pin 28 from the hole 30 (either in solid or in liquid form), a plug 34 of a high melting point material is inserted in a rebated portion 36. The plug should be an interference fit in the rebate 36, or should otherwise be securely fixed in the hole. However, it will be realized by those skilled in the art that at the normal operating temperatures of a gas turbine, a low melting point metal such as Cerrobend™ will be above its vaporization temperature and will therefore disappear entirely from within the recess 16 within a relatively short time, due to leakage past the sealing element 18.

In the present embodiment, it is assumed that the confronting faces 23, 24 are annular, and that the sealing element 18 is one of a number of sealing elements arranged in a circle extending around the confronting annular faces 23, 24. The number of sealing elements 18 may be few or many, according to the engineering requirements of the design. In this manner, the sealing arrangement is segmented, i.e., its circumference is divided into a number of lengths. The sealing elements will each be provided with at least one spring 26 and at least one latch 28 and be capable of sliding in and out of the component 12 independently of each other. Conveniently, the recess 16 may also be one of the same number of recesses for housing the individual sealing elements. The sealing elements and the recesses may be arcuate in the circumferential direction of the annular faces 23, 24, and this of course is essential unless the sealing element segments are very short in relation to the circumference of the seal arrangement.

The spring 26 in the drawings is of course shown diagrammatically and may comprise any one of several known types of spring. For example, if the sealing element 18 is short in the circumferential dimension, a single coil spring or leaf spring may suffice as spring 26, but if the sealing element is long in that dimension, a circumferential series of spaced-apart coil springs or leaf springs, or a circumferentially extending ripple spring, may be used.

Although the above description has focussed on an annular or part-annular seal for sealing between confronting annular faces in a turbine, the invention is not so restricted and is equally applicable to linearly extending seals for sealing between linearly extending faces. 

1. A sealing arrangement for acting across a gap between first and second machine components operating at elevated temperatures, comprising: a) at least one sealing element having a first end captured within the first component and a second end able to seal against a surface of the second component; b) spring means acting between the first component and the at least one sealing element to urge the at least one sealing element towards the second component; and c) retention means for temporarily retaining the at least one sealing element within outer dimensions of the first component, the retention means being temperature-sensitive and operative only once to release the at least one sealing element to perform its sealing function at a predetermined elevated temperature.
 2. The sealing arrangement according to claim 1, in which the temperature-sensitive retention means is at least one fusible detent that at the predetermined elevated temperature fails by one of softening and melting of the material of which it is made, thereby releasing the at least one sealing element.
 3. The sealing arrangement according to claim 1, in which the fusible detent comprises a fusible latch that is held in the first component and that projects into the at least one sealing element.
 4. The sealing arrangement according to claim 1, in which the temperature-sensitive retention means is at least one detent that at the predetermined elevated temperature fails by one of embrittlement and charring of the material of which it is made, thereby releasing the at least one sealing element.
 5. The sealing arrangement according to claim 2, in which the fusible detent comprises a pin.
 6. The sealing arrangement according to claim 1, in which the first and second components are annular and bound a gap between them by respective confronting annular faces of the first and second components, and a plurality of sealing elements are arranged in a circle that extends around the confronting annular faces.
 7. The sealing arrangement according to claim 6, in which the first and second components are gas turbine components.
 8. The sealing arrangement according to claim 6, in which the first and second components are internal casings of a gas turbine.
 9. A method of actuating a face seal between mutually confronting machine components in a machine capable of operation at elevated temperatures, comprising the step of: providing a temperature-sensitive retention means to enable a once-only actuation of the face seal after assembly of the machine when the machine components are operating at the elevated temperatures for the first time. 